The CNS 2387-1993 standard specifies a test method for paper opacity, using an 89% reflectance backing for measurement. The standard is applicable to all types of paper and is designed to evaluate the light transmission performance of paper and its suitability for printing, Encasement and Miscellaneous applications. The opacity test is performed by comparing the differences in reflectance of paper under different backing conditions, involving sample preparation, test instrument calibrating and operating steps. The standard specifies requirements for the test environment and measurement accuracy to ensure conformity and reliability of results. This standard provides a unified mass evaluation basis for paper manufacturers and users, which helps to optimize paper performance and improve its effectiveness and quality control in practical applications.